In a power semiconductor module, a surge voltage is generated at the time of switching of a switching device. A surge voltage is a voltage pulse generated in a short period of time. When a surge voltage is generated, a sudden voltage change is applied to a parasitic capacitance in the power semiconductor module, thus causing a noise current. The noise current is transmitted to the entire apparatus in which the power semiconductor module is included through parasitic components in the apparatus and causes a trouble, such as a malfunction. Further, an increase in surge voltage causes an increase in loss, and subsequent heat generation at a semiconductor device. Therefore, there is a risk of thermal destruction. Implementation of a highly heat-dissipative structure for avoiding thermal destruction would lead to an increase in cost.
PTD 1 (Japanese Patent No. 5550553) discloses a power semiconductor module that can reduce a surge voltage by reducing an effective inductance of the wires. Specifically, in the power semiconductor module in this document, semiconductor devices, i.e., a negative-side diode, a positive-side switching device, a negative-side switching device, and a positive-side diode, are arrayed in this order in a row on a substrate. According to this configuration, when switching of the positive-side switching device is performed, a surge current flows in two directions, i.e., clockwise and counterclockwise directions, through the negative-side diode and the negative-side switching device on both sides of the positive-side switching device. As a result, the magnetic flux is canceled, and the effective inductance of the current path can be reduced (see paragraph 0033 of PTD 1). Similarly, when switching of the negative-side switching device is performed, a surge current flows in two directions, i.e., clockwise and counterclockwise directions, through the positive-side switching device and the positive-side diode on both sides of the negative-side switching device. As a result, and the effective inductance of the current path can be reduced.